Cast nephropathy, or myeloma kidney, is an inflammatory tubulointerstitial renal lesion that occurs in the setting of multiple myeloma. Characteristically, multiple intraluminal proteinaceous casts are identified mainly in the distal portion of the nephrons. The casts are typically acellular, homogenous and eosinophilic with multiple fracture lines. Immunofluorescence and immunoelectron microscopy confirm that the casts contain light chain immunoglobulins and Tamm-Horsfall glycoprotein. Glomeruli are usually normal in appearance. Casts obstruct the flow of tubular fluid, producing obstruction and the clinical manifestations of renal failure. Persistence of the casts produces inflammation and tubular atrophy that typify myeloma kidney. The end result is end-stage kidney failure. Renal failure from this lesion may present acutely or as a chronic progressive disease and may develop at any stage of myeloma.